The present invention relates to rigid, closed-cell, flame resistant polyurethane foams and to a process for the production thereof.
Rigid, closed-cell polyurethane-rigid foams, which have a flame resistance in accordance with the fire classification B2 according to DIN 4102 have become increasingly more important in the building industry. Many proposals have been made over the years for producing polyurethane-rigid foams which have been rendered flame-resistant.
One proposal involves producing polyurethane foams which have polyisocyanurate structures. Structures of this type may be detected if more than 1.5 isocyanate equivalents for each hydroxyl equivalent (that is, the isocyanate-index is above 1,5) are reacted in the presence of trimerization catalysts. Foams of this type are not generally used, however, because they are often brittle and cannot be produced using all standard apparatus due to their sensitivity to the effects of heat during production.
Another process for producing flame-resistant polyurethane rigid foams requires use of a flame-proofing agent in the production of such foams. A distinction is generally made between reacting and non-reacting flame-proofing agents. If large quantities of non-reacting flame-proofing agents are used, a foam having poor properties is obtained. Large quantities of reacting flame-proofing agents are often low-functional and make the foam flexible. Relatively high functional flame-proofing agents produce high viscosities, which create difficulties when producing the foam.
German Offenlegungsschrift No. 31 01 748 for example, describes the relationships between the content of flame-proofing agent and behavior under fire and between the flame-proofing agent, hydroxyl number and hardening.